Devices for varying or changing the angular phase relation or timing between an engine camshaft and crankshaft are well known, as may be seen by reference to U.S. Pat. Nos. 3,626,720 and 4,754,727 which are both assigned to the assignee of this patent and which are both incorporated herein by reference.
The U.S. Pat. No. 3,626,720 to Meachem et al includes a helical ball spline mechanism for varying the phase relation in response to selective porting of engine oil pressure to axially displace a piston therein.
The U.S. Pat. No. 4,754,727 to Hampton discloses a device including an axially displaceable advancing plate drivingly interconnecting support and drive members via straight and angular lugs or splines. The advancing plate is threadably mounted on a drum for axial displacement along the drum in response to relative rotation between the drum and plate. Relative rotation in one direction is provided by a spring reacting between the hub and drum, and in the other direction by selective application of a frictional force for retarding rotation of the drum counter to the spring force.
As is known, the above mentioned phase change devices vary valve timing to improve engine operation. However, the above devices and other such devices have certain disadvantages which have prevented or limited their use in mass production. For example, they tend to be difficult to package in the space normally available, they tend to have prohibitive mechanical complexity, they tend to be unreliable, or they tend to be difficult to control.